1. Field of the Invention
This present invention relates to a structure of phase shifting mask. More particularly, this present invention relates to a structure of chrome phase shifting mask.
2. Description of the Prior Art
Photolithography plays a very important role in semiconductor manufacture, and mask is the most important element in photolithography. In the prior art, a well-known mask is the binary intensity mask (BIM). Referred to FIG. 1A, a binary intensity mask comprises a quartz layer 100 and a plurality of chrome areas 110 onto the quartz layer 100. Light is obstructed by the chrome areas 110. Thus, the transmission of the chrome areas 110 is 0%, and the transmission of the non-chrome areas of the quartz layer 100 is 100%. The E-field strength plot of light through the binary intensity mask is shown in FIG. 1B, and the intensity plot of a light on a wafer through the above-mentioned binary intensity mask is depicted in FIG. 1C.
Another well-known technology is phase shifting mask. Phase shifting mask is widely used for advanced photolithography. FIG. 2A is a half-tone phase shifting mask. The above-cited phase shifting mask comprises a quartz layer 200, and a plurality of shifter 210. The phase difference between the quartz layer 200 and the shifters 210 may be 90°, 180°, or 270°. The transmission of the shifters 210 is 3% to 20%, and the transmission of the quartz layer 200 without the shifters 210 is 100%. FIG. 2B depicts an E-field strength plot of light through the phase shifting mask. FIG. 2C depicts an intensity plot of a light on a wafer through the mask.
With the decreasing of the line width tolerance, the phase shifting mask is more and more important for controlling the line width. However, the materials of the phase shifting mask in the prior art may not be suitable for different wavelength light sources to develop due to the materials including different absorptions of different wavelengths. Thus the new shifter materials should always be found out for a new photolithography generation. When the wavelength of the light of the light source is different, it is difficult and complex for finding out a suitable shifter material for achieving the different phase requirement and the transmission requirement.
Hence, for improving the efficiency in photolithography, it is an important object to develop a phase shifting mask without changing the shifter materials while changing the light source, and achieving different transmission and phase difference requirement.